During recent years, digital hearing aids using fully digital signal processing have advanced on the market due to new and improved properties made possible by advanced digital signal processing algorithms.
The functionality of these digital hearing aids is based on digital signal processing which is typically carried out by a proprietary Digital Signal Processor (DSP) adapted to carrying out one or more signal processing algorithms of the input signals or the input signal from e.g. one or several microphones and/or teleccoils etc. so that an enhanced processed output signal has been optimally adapted to the specific hearing loss of the user.
The used proprietary Digital Signal Processor (DSP) can be a fixed wired type designed to carry out a particular signal processing algorithm or a predetermined selection of such algorithms, or it can be of a programmable type where the predetermined selection of signal processing algorithms are implemented by a computer program or software. In the latter embodiment, the software is at run-time loaded from a non-volatile memory of the hearing prosthesis to a suitable Program RAM storage space and then executed from the Program RAM.
Irrespective of the type, the DSP requires the processing of the algorithm to be controlled by a clock signal which, in turn, will typically be derived from a master clock generator. The clock signal furnished to a contemporary DSP typically has a frequency between 1-4 MHz. Since the power consumption of a digital CMOS circuits, among others, is proportional to the clock frequency by which it is controlled, it is desirable to, on the one hand, keep the clock frequency as low as possible to save power/effect while on the other hand, it is desirable to make the clock frequency as high as possible in order to support more advanced signal processing algorithms, such as noise reduction and adaptive feedback suppression etc.
Thus, there exists a need in the art for a DSP-based hearing aid, in which the actual clock frequency of the DSP processor is dynamically and adaptively adjustable.